1. Field of the Invention
This invention relates to a semiconductor pressure transducer comprising strain gauges having piezoresistance effect, formed integrally by injecting an impurity into the surface of a diaphragm made of a single crystal of semiconductor such as silicon.
2. Description of the Prior Art
A currently used semiconductor pressure transducer using a diaphragm of, for example, single crystal silicon has such a structure that the diaphragm is made to have a supporting portion and a pressure-responsive portion and strain gauge units are formed at selected positions in the surface of the pressure-responsive portion through diffusion technique. These strain gauge units are connected in the Wheatstone bridge circuit. Such a semiconductor pressure transducer can effectively convert a strain generated in the surface of the diaphragm into an electrical signal. This performance of the silicon diaphragm is based on the piezoresistance effect of the semiconductor. The semiconductor pressure transducer is superior to the strain gauge using metal conductor in sensitivity to a physical quantity which is applied to produce a strain therein and finally converted into an electrical output, but defective in that it gives greater non-linear output characteristics in conversion.
The "non-linearity" is defined as follows. Assuming that on an output characteristic curve representing the relationship between a pressure applied to the diaphragm and an output of the strain gauge unit due to the pressure, the output corresponding to zero pressure is given at a point V.sub.o and the output corresponding to a measurable maximum pressure is given at a point V.sub.max, the straight line connecting the point V.sub.o to the point V.sub.max will represent an output of an ideal strain gauge unit which exhibits a linear output characteristic. If the maximum value of the output difference between the output characteristic curve and the straight line is given by .DELTA.V, the non-linearity NL is given by an expression: EQU NL=.DELTA.V/V.sub.max -V.sub.o .times.100% . . . (1)
U.S. Pat. No. 4,050,313 discloses a semiconductor pressure transducer which is arranged to compensate for such nonlinearity. However, it has been found that the arrangement of the U.S. patent is unsatisfactory when the ambient temperature changes, since the ambient temperature affects the non-linearity as well as the output.